Photo-Resist with Floating Acid

ABSTRACT

A method for fabricating a semiconductor product includes applying a photo-resist layer to a substrate, the photo-resist layer including a higher acid concentration at an upper portion of the photo-resist layer than at a lower portion of the photo-resist layer. The method also includes exposing the photo-resist layer to a light source through a mask including a feature, the photo-resist layer including a floating, diffusing acid that will diffuse into a region of the photo-resist layer affected by the feature while not diffusing into a feature formed by the mask.

BACKGROUND

Photolithography is a common technique used in the manufacture ofsemiconductor products. Photolithography processes involve the formationof features by using a photo-mask to expose certain regions of aphoto-resist layer to light. The exposed or unexposed regions are thendeveloped away to expose a semiconductor layer underneath thephoto-resist. The exposed semiconductor layer can then have variousprocesses performed thereon such as etching or doping.

Conventional methods for improving resolution usually include using aquencher, photo decomposable base (PDB) or photo decomposable quencher(PDQ) and a photo-acid generator (PAG) in the photoresist layer. Thequencher is a base molecule that can neutralize the acid to quench achemically amplified reaction (CAR). The PDB or PDQ is a base andtypically becomes less basic after exposure. The PAG generates an acidafter exposure.

One way to selectively develop regions of a photo-resist material is toexpose certain regions to light through a mask. Some masks includescattering bars along the side of various features. The scattering barhelps with the exposure process. Nevertheless, the scattering bars canadversely affect the photo-resist material by blocking light where lightshould not be blocked. As a result, some or all of the scattering barscan printout onto the underlying area. It is thus desirable to be ableto use scattering bars while not causing printout from the scatteringbars onto the layer underneath the photo-resist layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a diagram showing an illustrative photo-resist exposureprocess, according to one example of principles described herein.

FIG. 2 is a diagram showing an illustrative acid diffusion process,according to one example of principles described herein.

FIGS. 3A and 3B are diagrams showing the difference between a hard masklayer with and without use of an acid diffusing photo-resist layer,according to one example of principles described herein.

FIGS. 4A-4C are diagrams showing illustrative top views of featuresformed with and without using a floating acid photo-resist, according toone example of principles described herein.

FIG. 5 is a flowchart showing an illustrative method for fabricating asemiconductor product, according to one example of principles describedherein.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Moreover,the performance of a first process before a second process in thedescription that follows may include embodiments in which the secondprocess is performed immediately after the first process, and may alsoinclude embodiments in which additional processes may be performedbetween the first and second processes. Various features may bearbitrarily drawn in different scales for the sake of simplicity andclarity. Furthermore, the formation of a first feature over or on asecond feature in the description that follows may include embodimentsin which the first and second features are formed in direct contact, andmay also include embodiments in which additional features may be formedbetween the first and second features, such that the first and secondfeatures may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

The present disclosure provides a lithography method for use inmanufacturing a semiconductor device. The terms lithography, immersionlithography, photolithography, and optical lithography may be usedinterchangeably in the present disclosure. Photolithography is a processused in microfabrication, such as semiconductor fabrication, toselectively remove parts of a thin film or a substrate. The process useslight to transfer a pattern (e.g., a geometric pattern) from a photomaskto a light-sensitive layer (e.g., photoresist, or simply “resist”) onthe substrate. The light causes a chemical change in exposed regions ofthe light-sensitive layer, which may increase or decrease solubility ofthe exposed regions. If the exposed regions become more soluble, thelight-sensitive layer is referred to as a positive photoresist. If theexposed regions become less soluble, the light-sensitive layer isreferred to as a negative photoresist. Baking processes may be performedbefore or after exposing the substrate, such as a post-exposure bakingprocess. A developing process selectively removes the exposed orunexposed regions with a developing solution creating an exposurepattern over the substrate. A series of chemical treatments may thenengrave/etch the exposure pattern into the substrate (or materiallayer), while the patterned photoresist protects regions of theunderlying substrate (or material layer). Alternatively, metaldeposition, ion implantation, or other processes can be carried out.Finally, an appropriate reagent removes (or strips) the remainingphotoresist, and the substrate is ready for the whole process to berepeated for the next stage of circuit fabrication. In a complexintegrated circuit (for example, a modern CMOS), a substrate may gothrough the photolithographic cycle a number of times.

FIG. 1 is a diagram showing an illustrative photo-resist exposureprocess. The process involves a substrate 102, a hard mask layer 104, apositive tone photo-resist layer 106, and a photo-mask 108. According tothe present example, the substrate 102 is a semiconductor substrate 102such as a semiconductor wafer or other suitable device. Thesemiconductor substrate 102 may be made from any suitable semiconductormaterial, and include various features such as various doped regions,dielectric features, and/or multilevel interconnects.

The hard mask layer 104 is used to protect certain regions of thesemiconductor substrate 102 from various photolithographic processessuch as etching and doping. A pattern is formed into the hard mask 104to allow the doping or etching processes to be selectively applied tothe substrate 102.

The photolithographic process involves the application of thephoto-resist layer 106. In the present example, the photo-resist layer106 is such that areas exposed to a light source 120 become insoluble toa developing solution. Specifically, the light causes a chemicalreaction in the photo-resist layer 106 that creates acid componentswithin the exposed region. The developing solution is selected so thatareas with acid will remain, while areas of the photo-resist layerwithout acid components are developed away. Such a developing solutionis a negative tone developing solution.

The exposure energy source may be a variety of sources, including a deepultra-violet (DUV) source. In one example, the energy source may be anExtreme UltraViolet (EUV) exposure. In some examples, other energysources such as electron beam (e-beam) writing. Alternatively, theexposure process may utilize other exposure beams, such as ion beam,x-ray, and other proper exposure energy.

The photo mask 108 is used to expose certain regions of the photo-resistlayer 106 to the light source 120 while blocking the light at regionsthat are intended to be developed away. Using such a mask, a lot morearea of the photo-resist is exposed to the light than is blocked. Thus,such a mask is often referred to as a bright field mask 108.

When forming pattern features in the nanometer range, issues arise inthe precision of a mask feature due to the wavelength of the light fromthe light source 120. One way to minimize such issues is through use ofa scattering bar 112. A scattering bar within a bright field mask 108 isa small line formed along a feature 110. For example, if a particularfeature 110 is a line, than scattering bars will be placed along thatline on both sides. This helps protect the area of the photo-resistlayer that is intended to be blocked from the light source 120.Moreover, higher precision features that are less prone to error may beformed the process window for the features is enlarged through use of ascattering bar 112.

Use of a scattering bar, however, may create some problems.Specifically, the scattering bar will also block light and form regions116 that are void of acid and will thus be developed away, which is notdesirable. In some cases, this can cause unintended features to beprinted onto the layer beneath the photo-resist layer, in this case, thehard mask layer 104. This is referred to as printout. Printout can leadto errors in the final semiconductor product. Thus it is desirable toreduce or eliminate this printout. While reducing the width of thescattering bars 112 can help, the width can only be reduced so much asthe mask approaches a minimum feature size.

According to certain illustrative examples, the photo-resist layer 106is such that a higher acid concentration is formed at the top of thelayer than at the bottom of the layer after exposure. This can be doneby having floating acid components 118 such as floating Photo AcidGenerator components. Thus, acid components tend to float towards thetop of the layer 106, causing a higher concentration towards the top.

FIG. 1 illustrates the photo-resist layer 106 in varying shades. Thewhite regions 114, 116 illustrate regions that were blocked from thelight source 120 and thus no acid was created. These regions will bedeveloped away with the appropriate developing solution. The shadedregions 120 represent regions that were exposed to light, causing anacid creating chemical reaction. The floating acid components 118 areshown for illustrative purposes, but do not represent an accuratelyscaled size of such components. There is a higher concentration offloating acid components 118 on the top of the layer 106 than at thebottom of the layer 106 because of the floating acid components.

FIG. 2 is a diagram showing an illustrative acid diffusion process 200.As mentioned above, the exposure to light creates a chemical reactionwithin the photo-resist layer that creates acid generating components.The acid makes the photo-resist layer insoluble to a particular type ofdeveloping solution. The mask is designed such that the features to beformed into the photo-resist are opaque and thus block light from alight source 120. The scattering bars, however, also block light in anundesired manner.

The floating acid components are such that they will diffuse into thesmaller acid void regions left by the scattering bars. While there willbe some diffusion into the region of the photo-resist that is intendedto be a feature 114, this diffusion will not be enough to adverselyaffect that feature 114.

FIG. 2 also uses different shades to represent different aspects. Again,the white regions 114 represent areas that are without acid. Likewise,the dark shaded regions represent areas that were exposed to the lightand thus are filled with acid. The lightly shaded regions 204, 206represent areas where the floating acid components diffused into theacid void regions. As illustrated, the smaller regions left by thescattering regions become filled with acid, and thus remain insoluble tothe appropriate developing solution. While there is some diffusion intothe features 114 formed by the mask, the diffusion does not adverselyaffect the feature 114. Particularly, the amount of diffusion is smallcompared to the overall size of the feature 114 and thus the featureremains substantially intact. Because there is still no acid in theregion of the feature 114, this region gets developed away, exposing thehard mask layer 104 underneath.

There are a number of mechanisms that may be used to cause the acidgenerator components to float up. In one example, the alkyl groups of astandard PAG component can be replaced with alkyl fluoride groups. Thealkyl fluoride groups may be straight, branch, cyclic, or anycombination thereof. The alkyl fluoride groups may contain at least twocarbon units for both the cation unit and the anion unit. In someexamples, an alkyl group is added, and then connected to an alkylfluoride group.

Examples of the PAG, that is, a compound capable of generating an acidupon exposure, are given below. It should be understood that they may beused alone or in admixture of two or more. Suitable PAGs include oniumsalts, selenium salts, phosphonium salts, iodinium, sulfonium salts,organic halogen compounds, O-nitrobenzylsulfonate compounds,N-iminosulfonate compounds, N-imidosulfonate compounds, diazosulfonatecompound, sulfonimide compounds, diazodisulfonate compounds, anddisulfone compounds.

In an exemplary embodiment, the PAG is represented by one of thefollowing structures:

R¹-R³³ may be the same or different and each represents a hydrogen atom,an alkyl group having 1 to 20 carbon atoms, an aminoalkyl group having 1to 20 carbon atoms, a hydroxyalkyl group having 1 to 20 carbon atoms, ora substituted or unsubstituted aryl group having 1 to 20 carbon atoms.R¹-R³³ may bind together to form a ring. X⁻ represents a counter ion,such as BF⁻⁴, AsF₆, PF⁻⁶, SBF₆, SiF⁻⁶, ClO⁻⁴, perfluoroalkanesulfonicacid anion, alkylsulfoni anion, armomatic sulfonic acid anion,benzesulfonic acid anion or triisopropylbenzenesulfonic anion, acondensed polycyclic aromatic sulfonic acid anion, or a dye containingsulfonic acid. Ar¹ and Ar² may be the same or different, eachrepresenting an unsubstituted or substituted aryl group. A represents anunsubstituted or substituted alkylene group, a substituted orunsubstituted alkylene group or a substituted or unsubstituted arylenegroup. I⁺ represents the iodonium ion. Y represents a chlorine orbromine atom.

In some examples, the acid generator components may be made to floatthrough use of a floating Thermal Acid Generator (TAG). The TAGcomponents may have the following formulas: RCOO—CH₂CF₂SO₃ ⁻H⁺, andRCOO—CH₂CF₂SO₃ ⁻(R¹)₄N⁺. The R represents a substituted or unsubstitutedlinear, branched, or cyclic alkyl group having 1 to 20 carbon atoms, ora substituted or unsubstituted aryl group having 6 to 14 carbon atoms,and R1 represents a hydrogen atom, a substituted or unsubstitutedlinear, branched, or cyclic alkyl group, alkenyl group, ozoalkyl grouphaving 1 to 10 carbon atoms, aryl group, aralkyl group, aryloxoalkylgroup having 6 to 18 carbon atoms.

Other forms of floating acid may be used. For example, various organicacids and free acids may be used in accordance with principles describedherein. Particularly, acids that tend to float up and cause diffusioninto smaller regions affected by a scattering bar during exposure by amask.

FIGS. 3A and 3B are diagrams 300 showing the difference between a hardmask layer 104 with and without use of an acid diffusing photo-resistlayer. FIG. 3A illustrates the example described above in which aphoto-resist with floating acid components is used. After thephoto-resist has been developed away, an etching process can beperformed on the hard mask. After the etching process, the photo-resistlayer is removed entirely, leaving the hard mask layer on top of thesubstrate. The hard mask layer 104 may be used to protect the substratefrom certain photolithographic processes that are intended for certainregions as defined by the patterns. As illustrated, a feature 302 withinthe pattern extends through the hard mask 104 to the substrate 102.There is no printout from the scattering bars.

FIG. 3B, alternatively, illustrates what may occur if the acid-diffusiondoes not move acid into regions blocked by the scattering bars.Specifically, those regions will become developed away, and in somecases, they may extend through the entire photo-resist material suchthat unwanted features 304 will be formed into the hard mask 104. Thiscan cause problems with further photolithographic processes applied tothe substrate 102.

FIGS. 4A-4C are diagrams showing illustrative top views of featuresformed with and without using a floating acid photo-resist. Using aphoto-resist with material with floating acid generator components mayprovide a number of benefits. For example, when using traditionalphotolithographic techniques, line ends may sometimes shrink. Theshrinking of line ends can be reduced by using a photo-resist inaccordance with principles described herein.

FIG. 4A is a diagram showing an illustrative mask 400 with two line endsthat may be prone to shrinking. The white area illustrates the opaqueregion 402 of the mask 400. The shaded regions represent transparentregions 404 of the dark field mask 400. These transparent regions areused to define features into the photo-resist material.

FIG. 4B is a diagram showing an illustrative top view of features formedinto the photo-resist material using traditional photolithographictechniques. According to the present example, the line ends of thefeatures 408 shrink in comparison to the mask features 406. In contrast,FIG. 4C is a diagram showing an illustrative top view of features formedinto a photo-resist material having properties described herein.Particularly, the floating acid reduces the shrinking that occurs at theline ends. As illustrated, the features 410 formed into the photo-resistmaterial more closely match the features 406 of the mask 400.

FIG. 5 is a flowchart showing an illustrative method 500 for fabricatinga semiconductor product. According to certain illustrative examples, amethod for fabricating a semiconductor product includes a step ofapplying 502 a positive tone photo-resist layer to a substrate. Themethod further includes a step of exposing 504 the photo-resist layer toa light source through a mask including a feature. The method furtherincludes a step of using 506 a negative tone developer to develop awayregions of the photo-resist layer that are without acid. Thephoto-resist layer includes floating acid components including one ormore of floating Photo Acid Generator (PAG) components, Thermal AcidGenerator (TAG) components, or an organic acid.

According to certain illustrative examples, a method for fabricating asemiconductor product includes applying a positive tone photo-resistlayer to a substrate, exposing the photo-resist layer to a light sourcethrough a mask including a feature, and using a negative tone developerto develop away regions of the photo-resist layer that are without acid.The photo-resist layer includes floating acid components including oneor more of floating Photo Acid Generator (PAG) components, Thermal AcidGenerator (TAG) components, or an organic acid According to certainillustrative examples, a photo-resist material includes floating acidcomponents including one or more of floating Photo Acid Generator (PAG)components, Thermal Acid Generator (TAG) components, or an organic acid.

According to certain illustrative examples, a method for fabricating asemiconductor product includes exposing a positive tone photo-resistlayer to a light source through a mask including a feature, the exposedphoto-resist layer including a higher acid concentration at an upperportion of the exposed photo-resist layer than at a lower portion of theexposed photo-resist layer. The method further includes using a negativetone developer to develop away regions of the photo-resist layer thatare without acid. The photo-resist layer includes floating acidcomponents to diffuse into a region of the photo-resist layer withoutacid due to being blocked from the light source by the feature.

It is understood that various different combinations of the above-listedembodiments and steps can be used in various sequences or in parallel,and there is no particular step that is critical or required.Additionally, although the term “electrode” is used herein, it will berecognized that the term includes the concept of an “electrode contact.”Furthermore, features illustrated and discussed above with respect tosome embodiments can be combined with features illustrated and discussedabove with respect to other embodiments. Accordingly, all suchmodifications are intended to be included within the scope of thisinvention.

The foregoing has outlined features of several embodiments. Those ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those of ordinary skill in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of thepresent disclosure, and that they may make various changes,substitutions and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method for fabricating a semiconductor product,the method comprising: applying a positive tone photo-resist layer to asubstrate; exposing the photo-resist layer to a light source through amask including a feature; and using a negative tone developer to developaway regions of the photo-resist layer that are without acid; whereinthe photo-resist layer includes floating acid components including oneor more of floating Photo Acid Generator (PAG) components, Thermal AcidGenerator (TAG) components, or an organic acid.
 2. The method of claim1, wherein the floating acid diffuses so as to fill in a region void ofacid due to being blocked from the light source by the feature.
 3. Themethod of claim 1, wherein the PAG components include alkyl fluoridegroups in place of alkyl groups.
 4. The method of claim 3, wherein thealkyl fluoride group includes at least 2 carbon units for both an anionunit and a cation unit.
 5. The method of claim 1, wherein the PAG isselected from the group consisting of onium salts, selenium salts,phosphonium salts, iodinium, sulfonium salts, organic halogen compounds,O-nitrobenzylsulfonate compounds, N-iminosulfonate compounds,N-imidosulfonate compounds, diazosulfonate compound, sulfonimidecompounds, diazodisulfonate compounds, and disulfone compounds.
 6. Themethod of claim 1, wherein a linking compound links the PAG componentsto photo-resist material components.
 7. The method of claim 1, whereinthe TAG components include one of the following formulas:RCOO—CH2CF2SO3−H+; andRCOO—CH2CF2SO3−(R1)4N+; wherein, R represents a substituted orunsubstituted linear, branched, or cyclic alkyl group having 1 to 20carbon atoms, or a substituted or unsubstituted aryl group having 6 to14 carbon atoms, and R1 represents a hydrogen atom, a substituted orunsubstituted linear, branched, or cyclic alkyl group, alkenyl group,ozoalkyl group having 1 to 10 carbon atoms, aryl group, aralkyl group,aryloxoalkyl group having 6 to 18 carbon atoms.
 8. The method of claim1, wherein the organic acid comprises an alkyl group and an acid groupwith one of acetic, sulfuric, nitric, iodic, or fluoric.
 9. Aphoto-resist material comprising: floating acid components including oneor more of floating Photo Acid Generator (PAG) components, Thermal AcidGenerator (TAG) components, or an organic acid.
 10. The material ofclaim 9, wherein the PAG components include alkyl fluoride groups inplace of alkyl groups.
 11. The material of claim 9, wherein the alkylfluoride group includes at least 2 carbon units for both an anion unitand a cation unit.
 12. The material of claim 9, wherein the PAG isselected from the group consisting of onium salts, selenium salts,phosphonium salts, iodinium, sulfonium salts, organic halogen compounds,O-nitrobenzylsulfonate compounds, N-iminosulfonate compounds,N-imidosulfonate compounds, diazosulfonate compound, sulfonimidecompounds, diazodisulfonate compounds, and disulfone compounds.
 13. Thematerial of claim 9, wherein a linking compound links the PAG componentsto photo-resist material components.
 14. The material of claim 9,wherein the TAG components include one of the following formulas:RCOO—CH2CF2SO3−H+; andRCOO—CH2CF2SO3−(R1)4N+; wherein, R represents a substituted orunsubstituted linear, branched, or cyclic alkyl group having 1 to 20carbon atoms, or a substituted or unsubstituted aryl group having 6 to14 carbon atoms, and R1 represents a hydrogen atom, a substituted orunsubstituted linear, branched, or cyclic alkyl group, alkenyl group,ozoalkyl group having 1 to 10 carbon atoms, aryl group, aralkyl group,aryloxoalkyl group having 6 to 18 carbon atoms.
 15. The material ofclaim 9, wherein the organic acid comprises an alkyl group and an acidgroup with one of acetic, sulfuric, nitric, iodic, or fluoric.
 16. Amethod for fabricating a semiconductor product, the method comprising:exposing a positive tone photo-resist layer to a light source through amask including a feature, the exposed photo-resist layer including ahigher acid concentration at an upper portion of the exposedphoto-resist layer than at a lower portion of the exposed photo-resistlayer; and using a negative tone developer to develop away regions ofthe photo-resist layer that are without acid; wherein the photo-resistlayer includes floating acid components to diffuse into a region of thephoto-resist layer without acid due to being blocked from the lightsource by the feature.
 17. The method of claim 16, wherein the floatingacid components include floating Photo Acid Generator (PAG) components.18. The method of claim 17, wherein the PAG components include alkylfluoride groups in place of alkyl groups.
 19. The method of claim 16,wherein the floating acid components include Thermal Acid Generator(TAG) components.
 20. The method of claim 1, wherein the floating acidcomponents include an organic acid.